The present invention relates to an adhesive cooling composition to be directly or indirectly applied to a subject including humans to cool the subject due to its latent heat in vaporization of water and a process for preparing the composition.
Conventional cooling bases for a cooling composition include, for example, gels or aqueous solutions of crosslinked polyethylene glycol (PEG), polyethylene oxide (PEO), polyvinyl alcohol (PVA), sodium carboxymethyl cellulose, polyacrylic acid, salts thereof, carboxyvinyl polymer (CVP) or the like.
The cooling composition is available in various forms such as a sheet having a cooling base sealed with a film of polyethylene, polypropylene or the like or a poultice comprising a non-woven fabric or like fabrics coated with a gel base. In recent years, a demand has been growing for poultice-type cooling products from the viewpoints of adhesion, fixation, convenience in use, heat-absorbing property and so on.
Generally the cooling base for use in such poultice-type cooling products are in the form of a gel which is superior in shape retentivity and adhesiveness. For this reason, it is very difficult to uniformly stir and knead the components of the cooling composition in the manufacture thereof. Because of this difficulty, there arise problems, for example, masses of components not dispersed well due to insufficient stirring and air bubbles incorporated into the gel base.
Attempts have been made in the art to overcome such problems using an organic solvent such as polyhydric alcohol in more than a specific amount to reduce the dispersion density of the base.
However, this method, although advantageous in giving a uniform gel composition, inevitably involves a decrease of water to be incorporated into the composition in an amount corresponding to the volume of the organic solvent, consequently failing to produce a cooling composition which can achieve a higher cooling effect.
The present invention was completed in view of the above situation.
It is an object of the present invention to provide an adhesive cooling composition in a gel form which stably contains a large amount of water and which is excellent in cooling effect and/or coolness-preserving effect.
The adhesive cooling composition of the invention is safely applicable without causing irritation to the subject to be cooled, especially human""s skins. The composition which is adhesive by itself can be conveniently fixed to a substrate (a subject to be cooled, including humans) without use of an aid such as an adhesive tape. A further advantage is that even when directly applied to the surface of a substrate, preferably to human""s skins, the composition can be removed without leaving any residue on the substrate.
It is another object of the invention to provide a process for preparing the foregoing adhesive cooling composition.
It is a further object of the invention to provide an adhesive cooling device in the form of a sheet which contains the above-mentioned cooling composition as a cooling base.
The present inventors conducted extensive research to prepare a uniform gel composition without giving masses of components not dispersed well due to insufficient stirring, when mixing a polyacrylic acid, a polyvalent metal and an aqueous solution. As a result, the inventors found that when the bubble component is removed from the aqueous solution by deaeration, stirring and kneading can be done with an improved efficiency and the components can be uniformly dispersed in the aqueous solution, whereby a uniform gel composition is obtained. The gel composition produced by this method has the components dispersed well in the aqueous solution and is uniform and substantially free of a bubble component, even if a conventional solvent such as polyhydric alcohol is used in a considerably low proportion to the aqueous solution (or even if such solvent is not used).
The adhesive cooling composition of the invention need not contain a solvent, e.g. polyhydric alcohol as an essential constituent (or it may contain a small amount of a solvent) and is free of air bubbles. Due to the absence of a solvent and freedom from air bubbles, a more amount of water can be accommodated in the cooling composition.
Based on the above-mentioned findings, the present inventors realized at once the increase of water content conventionally considered difficult, directing attention to both the production process and the formula and successfully developed an adhesive cooling composition having a high cooling effect.